Print screen frame tensioning system

ABSTRACT

The print screen frame tensioning system, generally rectangular in shape and fabricated from extruded rectangular tubular rails, when assembled, each side rail of the frame has a longitudinal one way channel, circular in cross sectional area, formed in each of the tubular rails for substantially the length of the tubular rails for receipt of a locking rod, the locking rod being axially serrated in order to accept a matching internally serrated standard wrench socket and the longitudinal channel being axially serrated, each locking rod having an additional internal tensioning fitting formed on both of its longitudinal ends for separate lateral tensioning.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fabric stretchers and more particularlyto an apparatus for tensioning and re-tensioning screen fabric for usein screen printing processing or the like.

2. Description of the Prior Art

Stretching frames are used for a wide variety of applications. Oneprevalent use for such frames is in the field of graphic arts. In themedium of oil painting, the canvass must be stretched into a taughtplane so the ink may be applied onto a firm and stationary surface.Frequently the frame used for such art is made of wood and the canvassis attached to one side and then pulled across to the opposite sidewhere it is anchored. Such frames may be fashioned so that a wedge maybe driven into each of the corners of the frame to provide tension forthe tightening of the canvas.

Printing screens may be used for transfer of inks for the creation of anart work or in the printing industry. Screen mesh as used in the screenprint industry is manufactured from polyester and is typically supportedand tensioned between opposing sides of a four sided frame. The mesh,when uniformly stretched in a taught plane, provides the foundation fora stencil. Printing ink is then forced through the open areas of thestencil by means of a blade or squeegee creating an image in the shapeof the stencil on the work piece positioned beneath the screen. Toachieve optimum results, several factors must be considered. The screenmust be maintained at the recommended working tension throughout theprint run so the pattern is transferred with accuracy. Tension variationmust be kept to a minimum. Off contact must be kept to a minimum.

During the printing stroke, the squeegee blade deflects the fabricdownwards forcing it into direct contact with the work piece during itspassage across the screen. This deflection causes the fabric to bestretched from its undisturbed condition. The constant cycle ofstretching and snapping back accelerates the deterioration of both thescreen and the stencil, especially if the panel is skewed duringinstallation. Proper tensioning decreases off contact, improves imagequality and provides longer stencil and image life. Additionally, as thescreen mesh undergoes these distorting forces during the print stroke,the stencil in the screen may also be distorted, especially if thecontact between the screen and the fabric is redundant. This can resultin a slightly distorted image on the work piece.

Typical tubular alloy frames used to stretch the screen mesh utilizetubes positioned on all four sides of the frame. The screen is pulledover these tubes and locked in place without the necessary squaringmeans. In doing so, the frame may become slightly distorted and thisdistortion can cause the off contact distance between the screen and thework piece to vary across the print area with a consequent reduction inprint quality.

The essence of re-tensioning is to maintain a specific tension value innewtons. The majority of screen frames currently available do not allowthe mesh and stencil to be easily removed and reinstalled on the frame.Consequently screens must be stored mounted on their frames betweenprint runs. Removal of the mesh and accurate reinstallation for lateruse represents an improvement over the prior art. Applicant's U.S. Pat.No. 6,739,079 addressed the aforesaid problems and this applicationrepresents a novel contribution to those teachings and the screenprinting industry.

OBJECTS OF THE INVENTION

An object of the present invention is to provide for a novel printscreen frame tensioning apparatus which allows for the accuratetensioning and re-tensioning of the screen.

A further object of the present invention is to provide for a novelprint screen frame tensioning apparatus which is easily assembled andhas few moving parts.

A still further object of the present invention is to provide for anovel print screen frame tensioning system which allows for the screento be stored for reuse without the necessity of maintaining the screenon the frame.

A still further object of the present invention is to provide aclassical cross sectionally square or rectangular rails which are easierto work with and provide superior support and sealing of the ink well.

A still further object of the present invention is to provide for anovel print screen frame tensioning apparatus which maintains its squareshape during tensioning.

A still further object of the present invention is to provide for alocking clutch which aids in tensioning and which allows the tensioninglock rod to rotate in only one direction.

SUMMARY OF THE INVENTION

The print screen frame tensioning system, generally rectangular in shapeand fabricated from extruded rectangular tubular rails, when assembled,each side rail of the frame has a longitudinal one way channel, circularin cross sectional area, formed in each of the tubular rails forsubstantially the length of the tubular rails for receipt of a lockingrod, the locking rod being axially serrated in order to accept amatching internally serrated standard wrench socket and the longitudinalchannel being axially serrated, each locking rod having an additionalinternal tensioning fitting formed on both of its longitudinal ends forseparate lateral tensioning, the frame having a plurality ofthroughbores in its side walls for receipt of a plurality of lockingbolts, the frame and print screen being assembled by placing theassembled frame on a support, first attaching the fabric edges to thelock rods, and secondly the lock rods to the frame spreading the screenor fabric material with the lock rods across the frame, positioning thelocking rods in their respective longitudinal channels in theirrespective tubular rails, and thirdly partially closing the railrecesses via the lock bolts, selectively engaging the exposed ends ofthe lock rods with a wrench to rotate them and thus cause tensionvertically on the screen or fabric panel, and further simultaneouslytightening the plurality of locking bolts in selective throughboresduring the tensioning process. Each lock rod having a locking clutchassociates therewith so as to lock the rod and to permit rod rotation inonly a single direction.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention will become apparentparticularly when taken in light of the following illustrations wherein:

FIG. 1 is a cross sectional view of the side rail including lock rod,lock strip, fabric and lock bolt;

FIG. 2 illustrates the top of all four rail members forming the framejoined to corner brackets;

FIG. 3 is a respective bottom view of assembled frame with fabric andlock rods in a pre-tensioning position;

FIG. 4 is an exploded view of the split lock rod;

FIG. 5 is a close up perspective top view of the frame corner;

FIG. 6 is a perspective bottom view of the frame at the start of thetensioning process; and

FIG. 7 is an exploded view of the locking clutch of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

Applicant in describing the invention herein will refer to surfaces asbeing upper or lower, upper being in the printing mode. In doing so theApplicant is referring to surfaces in the assembly phase of the screentensioning system. Those with skill in the art will recognize that inactual use the frame as assembled is inverted for the application of theprinting ink.

FIG. 2 is a perspective top view of the frame 10 of the presentinvention, and FIG. 3 is an exploded bottom perspective view of theframe 10 of the present invention with the mesh of fabric panel and thetensioning means.

The frame member 10 is generally rectangular and formed by four tubularside rails 12, 14, 16, and 18, rectangular in cross section, which arepreferably extruded and when attached to a corner unit form therectangular frame 10 using L-shaped corner brackets 20. The side railsare generally rectangular in cross section in the assembly position(bottom up) having an upper wall 21, a lower wall 22 inner side wall 24,and an outer side wall 26. The upper wall 21 is formed with openlongitudinal channel 28 of circular cross section adjacent outer sidewall 26. This longitudinal channel 28 of the tubular side rails is thereceptacle for the tensioning and locking mechanism for the print screenframe as more fully described hereafter.

FIG. 3 is a perspective exploded bottom view of the frame 10, fabric forscreen material 30 and the tensioning means. There is formed in upperwall 21, the tensioning and locking mechanism heretofore mentioned. Thetensioning mechanism comprises a longitudinal channel 28, circular incross section, formed in each of the tubular rails in upper wall 21.Each longitudinal channel 28 is designed to receive and accommodate alocking rod 34. Locking rod 34 is serrated 36 along its entire externalaxis, and both ends are threaded to accept fittings 38 which in the formshown is a threaded set screw shaped to accommodate an Allen wrench. Inthe embodiment illustrating the fitting 38 is an Allen head threadedscrew combination securing within a selectively threaded longitudinalpassageway 39 in each lock rod 34. The longitudinal channel 28 is alsoserrated 31 internally to cooperate with the external serrated surface36 of the entire locking rod 34. The outer side wall 26 and upper wall21 are not physically connected to each other, but are biased to someextent as exhibited in FIG. 3 with a longitudinal internal gap 40running the length of longitudinal channel 28. There is positioned inouter side wall 26 a plurality of apertures 41 aligned with apertures 42in inner side wall 24 (See FIG. 1) for receipt and accommodation of apinching threaded locking fastener 43 in the form of a threaded lockbolt.

In operation, the frame is placed on a support. First the lock rods areattached to the panel. The fabric or screen panel 30 is spread over theframe 10 with the lock rods attached. A locking strip 57 is insertedinto the Lock strip groove 56 overlying the fabric panel in order tosecurely grip and square the panel at each of its four edges. A lockingrod 34 is then positioned in each longitudinal channel 28 of the tubularrails 12, 14, 16, and 18 with the fabric or screen panel 30 betweenlocking rods 34 and longitudinal channel 28. The fitting ends 38 of eachlocking rod 34 is assessable at the exposed ends of each side rail dueto the particular construction of the corners. In this configuration,the screen or fabric panel 30 now extends over and winds around thelocking rod 34 in each of the tubular rails 12, 14, 16, and 18. Uponclosing the recesses 28 via the bolts 43, the ratchets or wrenches (notshown) can then selectively engage either or both ends 38 of the lockrod 34 with a set of socket wrenches so as to rotate the lock rod 34over the rod and vertically tension the screen or fabric panel 30.

FIG. 1 is a cross section of an assembled side rail with fabric orscreen panel and locking rods. The exterior serrations 36 in each of thelock rods 34 in cooperation with the one way internal serrations 31 inthe longitudinal channel 28 aids by engagement and frictionally that thelock rod cannot counter-rotate to decrease the tensioning while furtherinsured by the threaded locking pinching fasteners 43. In the manualmode each lock rod 34 would be sequentially rotated by use of a set ofwrenches or ratchets at each corner of the frame 10 and the pinchinglocking fasteners 43 would be simultaneously incrementally tightened. Itshould be noted that the channel serrations 28 are pointed against thedirection of rotation and ramped to the clockwise direction to prevent adegree of counter rotation.

The pinching locking fastener 43 in the form of lock bolts in apertures41 are selective tightened during rotation of lock rods 34 so as toclose the gap 40. Closing the gap 40 frictionally and mechanicallyprevents the selective lock rod 34 from counter-rotating to reduce thetension on the screen or fabric panel 30.

FIG. 1 is a cross sectional view of an assembled side rail 18 with bothtensioning means and fabric locking means 57 of the screen panel 30.This illustrates the locking rod 34 in position in longitudinal channel28 there being disposed therebetween the locking rod 34 and thelongitudinal channel 28 wall, the fabric or screen panel 30. Theinterior wall of longitudinal channel 28 has a plurality of one wayserrations or grooves 31 which cooperate with the serrations or grooves36 about the outer periphery of locking rod 34 and inner serrations ofthe wrench socket. FIG. 1, a cross sectional view, also illustratesthreaded locking pinching fasteners 43 extending between outer side wall26 and inner side wall 24. As the locking rod 34 is rotated to placevertical tension on the fabric or screen panel 30, threaded lockingpinching fasteners 43 are simultaneously tightened to narrow the gap 40so as to provide a locking means to provide proper vertical tension onthe fabric or screen panel 30 and to prevent the counter rotation oflocking rod 34.

Locking rod 34 could be used continuously, or as illustrated in FIG. 4,could be formed in a segmented or split fashion having a first end 34Aand a second end 34B and a connecting slide 50 slidably securable withinthe apertures of locking rod 34A and 34B thereby joining the two. Thefitting 38 for applying lateral tension would be the same in eitherlocking rod. The locking rod 34 design of the present invention wouldhave the aperture 39 which could be threaded to accept set screw 38within the locking rod formed of a central bore of a circular crosssection with a plurality of fingers 54 extending outwardly therefrom soas to cooperate with the lock rod fingers 52 within the locking rods 34Aand 34B in order to slidably secure same to each other. Locking rod 34is further formed with a lock strip groove 56 longitudinally formed onits outer surface accept the lock strip 57 and to aid in securing thepanel 30 to rod 34.

FIG. 5 is a perspective corner close up top view of a corner of theframe assembly illustrating the manner in which the user has access tothe exposed ends of each of the locking rods 34 at each of the cornersof the frame assembly 10.

FIG. 6 is a perspective bottom view of the frame assembly 10 of thepresent invention with the fabric or screen panel 30 in place and thelocking rods 34 positioned for the tensioning process.

It is essential to tension the entire dimension uniformly of thefabric/panel, avoiding the distortion and breakage caused when the panelis skewed and/or the corners become over-tensioned. The verticaltensioning means causes a back tension against the rods, the threadedlock pinch fasteners in conjunction, the lock ratcheting action in theclockwise direction prevents the fabric in its entirety from slippingback.

The print screen frame tensioning system of the present invention hasbeen further refined in order to insure that the locking rod 34 fromspring back of the panel during tensioning process is prevented. Thelock rod lock 60 acts as a one way clutch bearing and allows the lockrod 34 to be rotated in only one direction.

FIG. 7 is an exploded view of the lock rod lock 60 assembly. The lockrod lock 60 is comprised of two rings, one inner ring 62 and one outerring 64. The inner ring 62 engages the lock rod 34 and is complimentarybeveled on its interior surface 66 so as to be slidably engagable overthe lock rod 34. The outer ring 64 engages both the frame 28 and theinner ring 62. The outer ring 64 includes a plurality of L-shapedcutouts 68 which extend inwardly from one circumferential edge 70 of theouter ring 64. The plurality of L-shaped cutouts 68 define a pluralityof gripping contact surfaces 72 which are in the form of circumferentialfingers in which their terminal ends 74 are angled inwardly 76. Theinwardly angled 76 gripping contact surfaces 72 engage the serratedcircumference 78 of the inner ring 62 which is rotated contemporaneouslywith the lock rod 34. The inwardly angled gripper contact surfaces 72permit the lock rod 34 to be rotated in only one direction and thusprevent the spring back during the tensioning process.

The rail recesses as previously described are efficient in holding thelock rods 34 when properly pinched by the rail pinch bolts under normalcircumstances, but testing has shown that they are not one hundredpercent efficient for locking the lock rods 34 during and aftertensioning. The introduction of the lock rod locks 60 in the form of aone way clutch bearing assembly on each lock rod 34 enhances thetensioning process while allowing for panel security during use andstorage.

In most frames presently being used, the screen fabric has a tendency torelax and lose a portion of its tensioning value. With screens of theprior art, this could become a tedious task. A frame of the presentinvention allows the operator to increase the tension to maintain aparticular value without disturbing the frame assembly in any other way.With a frame of the present design, the operator makes the initialadjustment of tension using the locking rods and then locks them inplace with the lock bolts. A time period is allowed for the panel torelax and then it is returned to its proper tension. This is easilyaccomplished with a frame of the present invention in that the operatormerely loosens the locking pinching bolts and ratchets the locking rodsto the desired value on the locking bolts utilizing the lock rod locks60.

The frame and lock and tensioning means as described herein provides fora lower cost screen frame, mechanically soft corners, easy and fastassembly and easy re-tensioning with classic square rails, lock rods andfew bolts. The fabric may be treated in the lock area so that it may bememorized into shape and removed, stored, and reinstalled at a laterdate for reuse. Frames without re-tensioning presently used must bestored with the screen or fabric panel in place. This design allows forthe fabric or screen panel to be removed and stored separately so thatthe screen can be reused for another project.

While the present invention has been described with respect to theexemplary embodiments thereof, it will be recognized by those ofordinary skill in the art that many modifications or changes can beachieved without departing from the spirit and scope of the invention.Therefore it is manifestly intended that the invention be limited onlyby the scope of the claims and the equivalence thereof.

1. A screen stretching frame for stretching a screen fabric comprising:a means for tautly holding a screen fabric, comprising: a plurality oftubular frame members each having an open end, said tubular framemembers secured at their corners by corner brackets to form arectangular frame, each of said frame members having a longitudinalchannel, circular in cross section formed on an upper surface forreceipt therein of tensioning means, each of said tubular frame membershaving a plurality of threaded locking members positioned between sidewalls thereof transverse to said longitudinal channel and positionedbelow said longitudinal channel; and means for adjustably alteringtension on said screen fabric, said screen fabric laid across saidtubular frame members, said means for adjustably altering the tension ofsaid screen fabric comprising a tubular roller member positioned withineach of said longitudinal channels on said tubular frame members, saidtubular roller members sandwiching said screen fabric between saidlongitudinal channels and said tubular frame members, each of saidtubular frame members having a fitting at each end for lateral tensionand for rotation of said tubular member within said longitudinal channelfor engaging said screen fabric and vertically tensioning the same, saidplurality of locking members transverse to said longitudinal channelbeing simultaneously adjusted in tightness to compress said longitudinalchannel about said tubular roller member and said screen fabric untilthe desired tautness is achieved; said tubular roller member positionedwithin each of said longitudinal channels having at least one lockingmeans, said locking means comprising an inner circumferentially serratedring receivable on said tubular roller member, and rotatable therewith,an outer ring slidable over said inner ring, said outer ring having aplurality of L-shaped cuts on one circumferential edge defining aninwardly angled gripping contact surface engagable with said innercircumferentially serrated ring so as to permit rotation of said tubularroller member in a single direction.
 2. A screen stretching frame forstretching a screen fabric in accordance with claim 1 wherein each ofsaid tensioning members in the form of said tubular roller member isformed with a bore therethrough for receipt of a fitting member.
 3. Thescreen stretching frame for stretching a screen fabric in accordancewith claim 1 wherein each of said tubular roller members is formed witha grooved serrated outer surface, defining a plurality of groovespositioned in a longitudinal arrangement on said tubular roller member,said tubular roller member is further formed with a lock strip groove toaccept a fabric lock strip.
 4. The screen stretching frame forstretching a screen fabric in accordance with claim 1 wherein saidlongitudinal channel is formed with a grooved inner surface, defining aplurality of grooves arranged in a longitudinal orientation within saidlongitudinal channel and cooperative with said tubular roller member soas to prevent counter rotation of said tubular roller member achievingtautness of said screen fabric.
 5. The screen stretching frame forstretching a screen fabric in accordance with claim 1 wherein saidlongitudinal channel formed in each of said tubular frame members isformed with a longitudinal gap allowing compression of said longitudinalchannel by said locking members about said tubular roller member andsaid screen fabric thereby maintaining tautness.
 6. The screenstretching frame for stretching a screen fabric in accordance with claim1 wherein said screen fabric is removed from said screen stretchingframe by untightening said locking members and removing said tubularroller members from said longitudinal channels.
 7. A rectangularstretching frame for stretching a screen fabric comprising: the twopairs of straight frame tubes having open ends, each pair formingopposing sides of a rectangular stretching frame, each frame tubedefining a tube axis and having a longitudinal channel of circular crosssection formed in an upper surface thereof, each of said longitudinalchannels having a longitudinal gap running the length of saidlongitudinal channel; four rigid L-shaped corner brackets for securingsaid frame tubes for forming said rectangular stretching frame; fourmeans for tensioning, each tensioning means supported within saidlongitudinal channel and rotatable therein, each of said tensioningmeans having a fitting formed in both ends for lateral expansion; atubular roller member positioned within each of said longitudinalchannels having at least one locking means, said locking meanscomprising an inner circumferentially serrated ring receivable on saidtubular roller member, and rotatable therewith, an outer ring slidablyreceivable over said inner ring, said outer ring having a plurality ofL-shaped cuts on one circumferential edge defining an inwardly angledgripping contact surface engagable with said inner circumferentiallyserrated ring so as to permit rotation of said tubular roller member ina single direction; a plurality of second locking means formed in eachframe tube transverse to said longitudinal channel and positioned belowthereof for selective tightening and compression of said longitudinalchannel about said tensioning means, said screen fabric overlaid saidrectangular stretching frame and positioned within said longitudinalchannels and both secured and sandwiched between said tensioning meansand said tubular channel.
 8. The rectangular stretching frame inaccordance with claim 7 wherein said tensioning means comprises fourtubular roller members positioned in said longitudinal channels, each ofsaid tubular rollers having a longitudinal strip lock groove and groovedouter surface and a throughbore therethrough for said fitting.
 9. Therectangular stretching frame in accordance with claim 7 wherein saidlongitudinal channel is formed with a grooved inner surface, defining aplurality of grooves, said grooves arranged in a longitudinalorientation within said longitudinal channel and cooperative with saidtubular roller member so as to prevent counter rotation of said tubularroller member achieving tautness of said screen fabric.
 10. Therectangular stretching frame in accordance with claim 7 wherein saidlongitudinal channel formed in each of said tubular frame members isformed with a longitudinal gap allowing compression of said longitudinalchannel by locking members about said tubular roller member and saidscreen fabric thereby maintaining tautness.
 11. The rectangularstretching frame in accordance with claim 10 wherein said screen fabricis removed from said rectangular stretching frame by untightening saidlocking members and removing said tubular roller members from saidlongitudinal channels for storage.